A study of 24 hr pulsatile GH secretion, acute GH response to iv GHRH, and plasma IGF-I measurements in older men, before and after two weeks of either twice daily sc GHRH injections or constant sc GHRH infusions by portable pump, each repeated at 2 different doses, has been completed. We demonstrated that pulsatile GH secretion and serum IGF-I levels were low in older men, and increased into the range seen in normal young men after treatment with 2 mg of GHRH by injection and either dose by infusion. Diurnal pulsatile secretory variation appeared more physiological with GHRH injections than during infusions, in that infusion tended to raise the interpeak (basal) GH levels and to diminish amplitude of nocturnal GH secretory peaks. GHRH treatment also resulted in apparent phosphate retention, suggesting an increase in protein synthesis. There were no adverse effects. A study of 2 weeks or orally administered 50:50 arginine/lysine mixture vs. placebo on GH and IGF-I secretion in older men has shown no effects on spontaneous GH secretory pattern, GH responses to GHRH, and serum IGF-I levels, suggesting that oral amino acids may not be a useful GH-stimulating intervention in the elderly.
